Epidemiological studies have shown that mean blood pressure and the prevalence of hypertension both increase with age. A possible role for dietary sodium intake in the blood pressure increase in aging individuals has been documented, but little information is available concerning possible age-associated changes in circulating hormones that affect sodium transport across vascular smooth muscle. The present study assesses individual differences in levels of two circulating sodium-pump inhibiting hormones as predictors of age-associated changes in resting blood pressure. Morning supine blood pressure and endogenous ouabain and digitalis-like factor will be measured in participants in the Baltimore Longitudinal Study on Aging meeting the inclusion criteria. The study also investigates possible differences in circulating sodium-pump inhibitors as a function of race and gender. Data supporting the hypothesis of a positive correlation between resting blood pressure and circulating sodium-pump inhibitors could lead to pharmacological and nonpharmacological intervention in hypertension focusing on either or both of these sodium-pump inhibitors and their determinants.